1. Field of the Invention
The invention relates to electronic waveform recorders and, more particularly, to those that can record a plurality of analog or digital signals and can be triggered to record these signals in response to a change occurring in any one of these signals.
2. Description of the Prior Art
The development and maintenance of any digital system often requires initial and on-going analysis of a variety of digital signals; some of which represent inputs to the system, some of which are internal signals, and the remainder representing outputs generated by the system. However, for a variety of reasons, such an analysis can rarely be undertaken immediately upon the occurrence of any of these signals. Chief among these reasons is that any digital signal may exist for only a relatively short period of time and/or may occur only once on an infrequent basis. In addition, some digital signals, which are related in time may occur only at widely varying times.
Consequently, a variety of electrical devices have commercially appeared or at least have been proposed in the art for recording digital signals, i.e., digital signal patterns, for subsequent use in, for example, system analysis. Generally, these devices fall into two broad classes: oscilloscopes, and electronic recorders. Unfortunately, each class possesses a unique drawback which limits its utility.
Specifically, oscilloscopes rely on repetitive input signals, i.e., waveforms, to obtain a bright image. Recent advances involving storage oscilloscopes involve the incorporation of high speed memories for recording high speed pulses and also for replaying the recorded waveforms so as to obviate the need for repetitive application of these pulses to an input to the oscilloscope. However, the memory disadvantageously complicates the use of the oscilloscope and, due to its restricted capacity, limits the use of storage oscilloscopes in applications involving the recording of multiple signals occurring at widely varying times.
Another limiting feature of an oscilloscope is its restricted time base. In many current digital circuit designs, pulse widths in the microsecond range are commonplace and pulse widths on the order of several nanoseconds are often being increasingly used. Furthermore, infrequently occurring widely spaced pulses, having such an extremely narrow pulse width and which may in fact have a pulse spacing as wide as several seconds, are also quite common in current digital circuits. However, whenever a storage oscilloscope is set to record such a narrow pulse, the fastest usable total sweep time might be on the order of 10 microseconds. A longer sweep would make a nanosecond pulse so narrow as to be unobservable. The use of presently existing extremely high speed (100 nanosecond) delayed sweeps is only partially able to rectify this, since only one such sweep across the screen of the oscilloscope is usually available upon the occurrence of an input pulse. Hence storage oscilloscopes are only useful for examining and/or storing each separate pulse and/or adjacent pulses closely occurring in time. Consequently, storage oscilloscopes are generally disadvantageously unable to record pulses having a plurality of widths in the microsecond to nanosecond region with time delays between adjacent pulses extending more than several orders of magnitude greater.
Electronic recorders, on the other hand, rely on storing data in a digital memory by "clocking" the incoming signal at pre-selected time intervals. The stored signal can be subsequently retrieved for processing and/or display. Such a recorder, when used in conjunction with an oscilloscope allows the display of an infrequently occurring pulse by repetitively retrieving (replaying) the recorded pulse waveshape from the memory in order to produce a desired trace. Unfortunately, these digital memories, due to their limited capacities, can only accommodate signals occurring over extremely short time spans. Hence, a plurality of infrequently occurring digital pulses having narrow pulse widths cannot be recorded by such devices.
A single bit of information is represented by two states, namely a 0 or a 1. When an analog signal is converted to digital data a plurality of bits are used to represent the amplitude value of the analog signal. Electronic memories are used for the recording of both digital signals, where only the state is recorded, and analog signals where the waveform is recorded using a plurality of bits. The deficiencies described are found in both types of recording.
To a certain extent, these deficiencies in electronic recorders known to the art have been advantageously eliminated in the analog waveform recorder disclosed in my co-pending U.S. patent application entitled "Signal Controlled Waveform Recorder", Ser. No. 494,322, filed May 13, 1983now abandoned. Unfortunately, the relatively slow speed at which the analog comparison circuitry used in the data taking process contained therein operates significantly and disadvantageously limits the maxium speed of the input waveforms that can be recorded. Additionally, the analog conversion circuit is slow in comparison to the times encountered in many pulse measurements. The comparison method of this invention eliminates the deficiences and allows the recording of digital signals in the nanosecond range. Analog waveforms are also recorded in the microsecond and nanosecond ranges, limited only by the speed of the analog conversion.